We use DBan at work -
http://dban.sourceforge.net/ - you can get it as a bootcd or boot floppy image.
It has DoD and Gutmann wiping methods which in theory should be able to clear hard drives of all data. We tried it at work and only found files using a partition undelete program that should have been there such as formatting information etc.
I dont know how truely good they are against Professional Expensive undelete methods but I would have thought if they are using DoD methods it would be fairly good!
Oh yeah and its FREE!